1. Field of the Invention
For generation of inverse time characteristics for, for example, time-lag type over-current relays, it is known to approximate a desired time function by means of individual parts which are linear in pieces. These parts are linked together in break points and, by altering the inclination of the curve part located between two break points, the composite time function can be given its desired shape. This approximation of a desired time function is usually performed with a diode matrix in combination with an integrating circuit. The diodes included are given varying bias by means of a voltage divider in order that the positions of the desired break points may be obtained.
2. The Prior Art
This method has two disadvantages. One is that the current-voltage characteristic of the diode is not ideal, but the voltage drop across the doide is dependent on the current through the diode. The other disadvantage is that the diode voltage drop is strongly dependent on the temperature.